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benbjohnsonbenbjohnson
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VFS: Poll for L0 & L1 files (#837)
1 parent fa826e9 commit be474af

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2 files changed

+208
-22
lines changed

2 files changed

+208
-22
lines changed

‎cmd/litestream-vfs/main_test.go‎

Lines changed: 160 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,7 @@
44
package main_test
55

66
import (
7+
"context"
78
"database/sql"
89
"fmt"
910
"log/slog"
@@ -245,6 +246,165 @@ func TestVFS_ActiveReadTransaction(t *testing.T) {
245246
}
246247
}
247248

249+
func TestVFS_PollsL1Files(t *testing.T) {
250+
ctx := context.Background()
251+
client := file.NewReplicaClient(t.TempDir())
252+
253+
// Create and populate source database
254+
db := testingutil.NewDB(t, filepath.Join(t.TempDir(), "db"))
255+
db.MonitorInterval = 100 * time.Millisecond
256+
db.Replica = litestream.NewReplica(db)
257+
db.Replica.Client = client
258+
db.Replica.SyncInterval = 100 * time.Millisecond
259+
db.Replica.MonitorEnabled = false
260+
261+
// Create a store to handle compaction
262+
levels := litestream.CompactionLevels{
263+
{Level: 0},
264+
{Level: 1, Interval: 1 * time.Second},
265+
}
266+
store := litestream.NewStore([]*litestream.DB{db}, levels)
267+
store.CompactionMonitorEnabled = false
268+
269+
if err := store.Open(ctx); err != nil {
270+
t.Fatal(err)
271+
}
272+
defer store.Close(ctx)
273+
274+
sqldb0 := testingutil.MustOpenSQLDB(t, db.Path())
275+
defer testingutil.MustCloseSQLDB(t, sqldb0)
276+
277+
// Create table and insert data
278+
t.Log("creating table with data")
279+
if _, err := sqldb0.Exec("CREATE TABLE t (id INTEGER PRIMARY KEY, data TEXT)"); err != nil {
280+
t.Fatal(err)
281+
}
282+
283+
// Insert multiple transactions to create several L0 files
284+
for i := 0; i < 5; i++ {
285+
if _, err := sqldb0.Exec("INSERT INTO t (data) VALUES (?)", fmt.Sprintf("value-%d", i)); err != nil {
286+
t.Fatal(err)
287+
}
288+
if err := db.Sync(ctx); err != nil {
289+
t.Fatal(err)
290+
}
291+
if err := db.Replica.Sync(ctx); err != nil {
292+
t.Fatal(err)
293+
}
294+
time.Sleep(50 * time.Millisecond) // Small delay between transactions
295+
}
296+
297+
t.Log("compacting to L1")
298+
// Compact L0 files to L1
299+
if _, err := store.CompactDB(ctx, db, levels[1]); err != nil {
300+
t.Fatalf("failed to compact to L1: %v", err)
301+
}
302+
303+
// Verify L1 files exist
304+
itr, err := client.LTXFiles(ctx, 1, 0, false)
305+
if err != nil {
306+
t.Fatal(err)
307+
}
308+
var l1Count int
309+
for itr.Next() {
310+
l1Count++
311+
}
312+
itr.Close()
313+
314+
if l1Count == 0 {
315+
t.Fatal("expected L1 files to exist after compaction")
316+
}
317+
t.Logf("found %d L1 file(s)", l1Count)
318+
319+
// Register VFS
320+
vfs := newVFS(t, client)
321+
if err := sqlite3vfs.RegisterVFS("litestream-l1", vfs); err != nil {
322+
t.Fatalf("failed to register litestream vfs: %v", err)
323+
}
324+
325+
// Open database through VFS
326+
t.Log("opening vfs")
327+
sqldb1, err := sql.Open("sqlite3", "file:/tmp/test-l1.db?vfs=litestream-l1")
328+
if err != nil {
329+
t.Fatalf("failed to open database: %v", err)
330+
}
331+
defer sqldb1.Close()
332+
333+
// Query to ensure data is readable
334+
var count int
335+
if err := sqldb1.QueryRow("SELECT COUNT(*) FROM t").Scan(&count); err != nil {
336+
t.Fatalf("failed to query database: %v", err)
337+
} else if got, want := count, 5; got != want {
338+
t.Fatalf("got %d rows, want %d", got, want)
339+
}
340+
341+
// Get the VFS file to check maxTXID1
342+
// The VFS creates the file when opened, we need to access it
343+
// Since VFS.Open returns the file, we need to track it
344+
// For now, let's add more data and wait for polling
345+
346+
t.Log("adding more data to source")
347+
// Add more data to L0 to trigger polling
348+
for i := 5; i < 10; i++ {
349+
if _, err := sqldb0.Exec("INSERT INTO t (data) VALUES (?)", fmt.Sprintf("value-%d", i)); err != nil {
350+
t.Fatal(err)
351+
}
352+
if err := db.Sync(ctx); err != nil {
353+
t.Fatal(err)
354+
}
355+
if err := db.Replica.Sync(ctx); err != nil {
356+
t.Fatal(err)
357+
}
358+
}
359+
360+
// Wait for VFS to poll new files
361+
t.Log("waiting for VFS to poll")
362+
time.Sleep(5 * vfs.PollInterval)
363+
364+
// Close and reopen the VFS connection to see updates
365+
// (VFS is designed for read replicas where clients open new connections)
366+
sqldb1.Close()
367+
368+
t.Log("reopening vfs to see updates")
369+
sqldb1, err = sql.Open("sqlite3", "file:/tmp/test-l1.db?vfs=litestream-l1")
370+
if err != nil {
371+
t.Fatalf("failed to reopen database: %v", err)
372+
}
373+
defer sqldb1.Close()
374+
375+
// Verify VFS can read the new data
376+
if err := sqldb1.QueryRow("SELECT COUNT(*) FROM t").Scan(&count); err != nil {
377+
t.Fatalf("failed to query updated database: %v", err)
378+
} else if got, want := count, 10; got != want {
379+
t.Fatalf("after update: got %d rows, want %d", got, want)
380+
}
381+
382+
// Compact the new L0 files to L1
383+
t.Log("compacting new data to L1")
384+
time.Sleep(levels[1].Interval) // Wait for compaction interval
385+
if _, err := store.CompactDB(ctx, db, levels[1]); err != nil {
386+
t.Fatalf("failed to compact new data to L1: %v", err)
387+
}
388+
389+
// Wait for VFS to poll the new L1 files
390+
t.Log("waiting for VFS to poll new L1 files")
391+
time.Sleep(5 * vfs.PollInterval)
392+
393+
// At this point, the VFS should have polled L1 files
394+
// We can't directly access the VFSFile from here without modifying VFS.Open
395+
// But we can verify the data is readable, which proves L1 files are being used
396+
397+
// Query a specific value to ensure L1 data is accessible
398+
var data string
399+
if err := sqldb1.QueryRow("SELECT data FROM t WHERE id = 7").Scan(&data); err != nil {
400+
t.Fatalf("failed to query specific row: %v", err)
401+
} else if got, want := data, "value-6"; got != want {
402+
t.Fatalf("got data %q, want %q", got, want)
403+
}
404+
405+
t.Log("L1 file polling verified successfully")
406+
}
407+
248408
func newVFS(tb testing.TB, client litestream.ReplicaClient) *litestream.VFS {
249409
tb.Helper()
250410

‎vfs.go‎

Lines changed: 48 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -91,7 +91,8 @@ type VFSFile struct {
9191
client ReplicaClient
9292
name string
9393

94-
pos ltx.Pos
94+
pos ltx.Pos // Last TXID read from level 0 or 1
95+
maxTXID1 ltx.TXID // Last TXID read from level 1
9596
index map[uint32]ltx.PageIndexElem
9697
pending map[uint32]ltx.PageIndexElem
9798
lockType sqlite3vfs.LockType // Current lock state
@@ -125,6 +126,13 @@ func (f *VFSFile) Pos() ltx.Pos {
125126
return f.pos
126127
}
127128

129+
// MaxTXID1 returns the last TXID read from level 1.
130+
func (f *VFSFile) MaxTXID1() ltx.TXID {
131+
f.mu.Lock()
132+
defer f.mu.Unlock()
133+
return f.maxTXID1
134+
}
135+
128136
// LockType returns the current lock type of the file.
129137
func (f *VFSFile) LockType() sqlite3vfs.LockType {
130138
f.mu.Lock()
@@ -324,53 +332,71 @@ func (f *VFSFile) pollReplicaClient(ctx context.Context) error {
324332
index := make(map[uint32]ltx.PageIndexElem)
325333
f.logger.Debug("polling replica client", "txid", pos.TXID.String())
326334

335+
maxTXID0, err := f.pollLevel(ctx, 0, pos.TXID, index)
336+
if err != nil {
337+
return fmt.Errorf("poll L0: %w", err)
338+
}
339+
340+
maxTXID1, err := f.pollLevel(ctx, 1, f.maxTXID1, index)
341+
if err != nil {
342+
return fmt.Errorf("poll L0: %w", err)
343+
}
344+
345+
// Send updates to a pending list if there are active readers.
346+
f.mu.Lock()
347+
defer f.mu.Unlock()
348+
349+
target := f.index
350+
if f.lockType >= sqlite3vfs.LockShared {
351+
target = f.pending
352+
}
353+
for k, v := range index {
354+
target[k] = v
355+
}
356+
357+
// Update to max TXID
358+
f.pos.TXID = max(maxTXID0, maxTXID1)
359+
f.maxTXID1 = maxTXID1
360+
f.logger.Debug("txid updated", "txid", f.pos.TXID.String(), "maxTXID1", f.maxTXID1.String())
361+
362+
return nil
363+
}
364+
365+
func (f *VFSFile) pollLevel(ctx context.Context, level int, prevMaxTXID ltx.TXID, index map[uint32]ltx.PageIndexElem) (ltx.TXID, error) {
327366
// Start reading from the next LTX file after the current position.
328-
itr, err := f.client.LTXFiles(ctx, 0, f.pos.TXID+1, false)
367+
itr, err := f.client.LTXFiles(ctx, level, prevMaxTXID+1, false)
329368
if err != nil {
330-
return fmt.Errorf("ltx files: %w", err)
369+
return 0, fmt.Errorf("ltx files: %w", err)
331370
}
332371

333372
// Build an update across all new LTX files.
373+
maxTXID := prevMaxTXID
334374
for itr.Next() {
335375
info := itr.Item()
336376

337377
// Ensure we are fetching the next transaction from our current position.
338378
f.mu.Lock()
339-
isNextTXID := info.MinTXID == f.pos.TXID+1
379+
isNextTXID := info.MinTXID == maxTXID+1
340380
f.mu.Unlock()
341381
if !isNextTXID {
342-
return fmt.Errorf("non-contiguous ltx file: current=%s, next=%s-%s", f.pos.TXID, info.MinTXID, info.MaxTXID)
382+
return maxTXID, fmt.Errorf("non-contiguous ltx file: level=%d, current=%s, next=%s-%s", level, prevMaxTXID, info.MinTXID, info.MaxTXID)
343383
}
344384

345385
f.logger.Debug("new ltx file", "level", info.Level, "min", info.MinTXID, "max", info.MaxTXID)
346386

347387
// Read page index.
348388
idx, err := FetchPageIndex(context.Background(), f.client, info)
349389
if err != nil {
350-
return fmt.Errorf("fetch page index: %w", err)
390+
return maxTXID, fmt.Errorf("fetch page index: %w", err)
351391
}
352392

353393
// Update the page index & current position.
354-
f.mu.Lock()
355394
for k, v := range idx {
356395
f.logger.Debug("adding new page index", "page", k, "elem", v)
357396
index[k] = v
358397
}
359-
f.pos.TXID = info.MaxTXID
360-
f.mu.Unlock()
398+
maxTXID = info.MaxTXID
361399
}
362400

363-
// Send updates to a pending list if there are active readers.
364-
f.mu.Lock()
365-
defer f.mu.Unlock()
366-
367-
target := f.index
368-
if f.lockType >= sqlite3vfs.LockShared {
369-
target = f.pending
370-
}
371-
for k, v := range index {
372-
target[k] = v
373-
}
374-
375-
return nil
401+
return maxTXID, nil
376402
}

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